This invention relates generally to imaging systems and specifically to scintillator pixel geometries.
In CT imaging systems, an x-ray source projects a fan-shaped beam that is collimated to lie within an X-Y plane, generally referred to as an “imaging plane”, of a Cartesian coordinate system toward an array of radiation detectors, wherein each radiation detector includes a detector element disposed within the CT system so as to receive this fan-shaped beam. An object, such as a patient, is disposed between the x-ray source and the radiation detector to lie within the imaging plane and thus is subjected to the x-ray beam, which passes through the object. As the x-ray beam passes through the object, the x-ray beam becomes attenuated before impinging upon the array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is responsive to the attenuation of the x-ray beam by the object, wherein each detector element produces a separate electrical signal responsive to the beam intensity at the detector element location. These electrical signals are referred to as x-ray attenuation measurements or x-ray images.
The x-ray source and the detector array may be rotated, with a gantry within the imaging plane, around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a “view”. A “scan” of the object comprises a set of views made at different gantry angles during one revolution of the x-ray source and the detector array. In an axial scan, the projection data is processed so as to construct an image that corresponds to a two-dimensional slice taken through the object. In CT systems that employ a single detector array, the slice thickness is controlled and determined by the width of the collimator, while in CT systems that employ a multiple detector array, the slice thickness is controlled and determined by summing the contributions of a plurality of detector sub-units and by physically moving the collimator to the outer edges of each slice.
Generally, the edges of a scintillation pixel are x-ray shielded so that they become insensitive to an x-ray beam regardless of the beam's angle or focal spot motion in the x or z-direction. One method of x-ray shielding pixel edges includes, positioning alternating tungsten wires in the x-direction and over pixel edges to prevent x-ray beams from reaching normally non-scintillating areas, e.g., gaps between pixels, such as the pixel edges, and the like. However, such methods may result in a reduction of spatial image resolution and light output resultant from the blockage of otherwise scintillating areas. Therefore, there is a need in the art controlling scintillator pixel geometries to reduce excessive x-ray beam-pixel contact, while avoiding an excessive reduction in spatial resolution by removing the shielding wires.